1. Field of the Invention
The present invention relates to a magnetic head and, more particularly, a composite magnetic head which has an inductive element and a magnetoresistive element and is incorporated into a magnetic recording/reproducing device such as a magnetic disc drive, a magnetic tape drive, etc.
2. Description of the Prior Art
In the technical field of a magnetic disc drive, a magnetic tape drive, etc., a composite magnetic head in which a recording head and a reproducing head are provided separately has been used to achieve a higher magnetic recording density and a higher speed recording/reproducing operation.
The composite magnetic head has a structure in which an induction type head having a spiral coil is superposed on a reproducing head using a magnetoresistive element (referred to as an "MR head" hereinafter). Both the recording and reproducing operations can be effected by the induction type head, but in general the induction type head of the composite magnetic head has been used only for the recording operation. The composite magnetic heads can be classified into a joint type and a separate type according to a difference whether or not a part of a magnetic pole of the induction type head is used commonly as an upper magnetic shielding layer of the MR head.
As shown in FIG. 1A, the joint type composite magnetic head is formed to have such a structure that an upper magnetic shielding layer 101 of an MR head 100 can execute commonly a function of a lower magnetic pole of an induction type head 110. The MR head 100 comprises the upper magnetic shielding layer 101, a lower magnetic shielding layer 102, and a magnetoresistive element 103. The magneto-resistive element 103 is isolated from the upper magnetic shielding layer 101 and the lower magnetic shielding layer 102 by an insulating layer 104. The induction type head 110 includes a spiral coil 111 a part of which is covered with an insulating layer 112. A part of the spiral coil 111 is surrounded by a magnetic pole which is composed of the upper magnetic shielding layer 101 and an upper magnetic pole 113.
As shown in FIG. 1B, the separate type composite magnetic head is formed to have such a structure that an upper magnetic shielding layer 121 of an MR head 120 is separated from a lower magnetic pole 131 of the induction type head 130. The MR head 120 comprises an upper magnetic shielding layer 121, a lower magnetic shielding layer 122, and a magnetoresistive element 123. The magnetoresistive element 123 is isolated from the upper magnetic shielding layer 121 and the lower magnetic shielding layer 122 by an insulating layer 124. In the induction type head 130, a part of the spiral coil 131 which is covered with an insulating layer 132 is surrounded by a loop magnetic pole. The magnetic pole consists of a lower magnetic pole 131 and an upper magnetic pole 133.
A recording gap g is formed in the magnetic poles over the magnetoresistive element 103. Similarly, the recording gap g is formed in the magnetic poles over the magnetoresistive element 123. The magnetic field generated from the spiral coil 111 is passed through the magnetic pole, and then output as the recording magnetic field to a magnetic recording medium (not shown) from the recording gap g. Similarly, the magnetic field generated from the spiral coil 131 is passed through the magnetic pole, and then output as the recording magnetic field to the magnetic recording medium (not shown) from the recording gap g.
In the joint type composite magnetic head, if a step-like unevenness or projection resides below the spiral coil 111, the spiral coil 111 is cut or broken away by the step-like projection when the spiral coil 111 is formed, otherwise the spiral coil 111 is made thinner by the presence of the step-like projection to result in an increase of electric resistance. In addition, lead wirings to be connected to the magnetoresistive element 103 of the MR head is cut or broken away or made thinner by the step-like projection. The same is true of the separate type composite magnetic head.
For this reason, in the joint type composite magnetic head, difference in level caused below the spiral coil 111 is made small by extending the lower magnetic shielding layer 102 up to a rear side area of the joint type composite magnetic head in which the magnetic pole 113 is not present and which is remote from the magnetoresistive element 103. Similarly, in the separate type composite magnetic head, difference in level step caused below the spiral coil 131 is reduced by extending the upper magnetic shielding layer 121 up to a rear side area of the separate type composite magnetic head in which both the upper magnetic pole 133 and the lower magnetic pole 134 are not present and which is remote from the magnetoresistive element 123.
In the joint type composite magnetic head, when a high frequency magnetic field is generated by feeding a high frequency recording current to the spiral coil 113, magnetic fields leaked from the magnetic pole are passed through the lower magnetic shielding layer 102 of the MR head 100. In the same manner, in the separate type composite magnetic head, when a high frequency magnetic filed is generated by feeding a high frequency recording current to the spiral coil 123, magnetic fields leaked from the magnetic pole are passed through the upper magnetic shielding layer 121 of the MR head 120.
However, as the frequency of the magnetic field passing through the lower magnetic shielding layer 102 or the upper magnetic shielding layer 121 is increased, an eddy current generated by the lower magnetic shielding layer 102 or the upper magnetic shielding layer 121 is increased. As a consequence, an efficiency in generating the recording magnetic field is decreased because the lower magnetic shielding layer 102 or the upper magnetic shielding layer 121 acts as a part of the magnetic path.